Slotted microstrip line for impedance matching having two stops to prevent ohmic contact between the movable reactive element and the center strip

ABSTRACT

Reactor for cancelling the reactances of a circuit by adding to it a conjugate reactance, involving at least one trolley that can be moved along a microstrip and supporting a probe whose penetration can be adjusted by a screw. One of the ends of the microstrip is terminated by a plug specially adapted to receive a transistor electrode.

United States Patent Louvel [54] SLOTTED MICROSTRIP LINE FOR IMPEDANCE MATCHING HAVING TWO STOPS TO PREVENT OHMIC CONTACT BETWEEN THE MOVABLE REACTIVE ELEMENT AND THE CENTER STRIP [72] lnventor:

[73] Assignee: Compagnie Industrielle des Telecommunications Cit-Alcatel, Paris, France [22] Filed: April 14, 1971 [2]] Appl. No.: 133,937

Guy Louvel, Antony, France [52] US. Cl. ..333/84 M, 333/33, 333/97 R, 324/58 [51] Int. Cl. .H01p 3/08, HOlp 5/08 [58] Field of Search.333/33, 84 M, 97 R, 73 S, 73 C, 333/73 W, 96, 97 R, 84, 81 A, 95; 324/58 A,

[56] References Cited UNITED STATES PATENTS 2,267,539 12/1941 Thorne ..333/97 2,433,817 12/1947 Rochester ..333/9 2,436,427 2/1948 Ginzton ..333/33 2,670,461 2/1954 Learned ..333/33 2,734,170 2/1956 Englemann et al. .....333/33 X 2,762,017 9/ 1956 Bradburd et a1 ..333/9 2,896,177 7/1959 Wilson ..333/84 M X 3,166,725 l/l965 Engen ..333/33 3,629,742 12/1970 Dayo ..333/97 R X FOREIGN PATENTS OR APPLICATIONS 130,561 5/1946 Australia ..333/97 1,149,134 12/1957 France ..333/84 M 699,379 11/1953 Great Britain ..333/33 770,303 3/1957 Great Britain ..333/97 OTHER PUBLICATIONS Stinehelfer, l-l. Strip Transmission Lines The Microwave Jr. Handbook & Buyer s Guide, 1969, pp. 69

Primary Examiner-Herman Karl Saalbach Assistant ExaminerWm. H. Punter Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT Reactor for cancelling the reactances of a circuit by adding to it a conjugate reactance, involving at least one trolley that can be moved along a microstrip and supporting a probe whose penetration can be adjusted by a screw. One of the ends of the microstrip is terminated by a plug specially adapted .to receive a transistor electrode.

5 Claims, 3 Drawing Figures PATENTEDHBTIOIBYZ I 3.697.902

SHE? 1 BF 2 I FIG/1 P'A'IENTEDncr-w I972 3.697.902

' SHEET 2 BF 2 lmi FIG. 3

Illa 17 I 8 d 10 20 a quil lfl 1. [him 23 SLOTTED MICROSTRIP LINE FOR IMPEDANCE MATCHING HAVING TWO STOPS TO PREVENT Ol-IMlIC CONTACT BETWEEN THE MOVABLE REACTIVE ELEMENT AND THE CENTER STRIP BACKGROUND OF THE INVENTION This invention relates to a reactor permitting the adaptation of active circuits, such as those of power transistors operating at very high frequencies.

ln known devices of this kind, we neutralize the reactance presented by the circuit and we adapt a signal, having a certain frequency, by adding a certain reactance at the end of a certain length of line.

We know in effect that the cancellation of the imaginary terms of a complex number can be obtained by adding conjugate imaginary terms. In this way we get only real terms.

ln this case, the adaptation of a circuit, presenting only resistive terms, is made possible, either in the direction of the input supplied by a resistive source, or in the direction of the output loaded by a resistance. Therefore, we can avoid a disadaptation which would bring in stationary waves and these waves cause losses in the actually available power. If the circuits, which we want to adapt, are transistor circuits, the corrections made will make it possible to protect them against destruction, particularly in the case of high power. Since the impedances of the transistors depend on the level of the applied signal, the measurements must be made at low power in order not to cause a deterioration of the transistor and the measurements must then be made at growing power so as to approach actual operating conditions. The method used generally also consists in placing between the transistor input and the signal generator a so-called upstream reactor, preceded by a coupler in conjunction with a bolometer and, between the transistor output and the resistive load, another reactor, called a downstream reactor, followed by another bolometer. These two reactors are first of all regulated at low power. We regulate the upstream reactor until we getthe biggest incident power; we then regulate the downstream reactor until we get the biggest output power. We thus tend to approach nominal power input and output conditions; the transistor is polarized at the voltage indicated by the manufacturer. Then we raise the power furnished by the generator and we continue to perfect the regulation of the reactors. Once these reactors have been adjusted at full power, we separate the assembly and measure the incidence presented by each reactor with a measurement line. We thus get the value of the combined conjugate impedances of the impedancespresented by the transistor at the input and the output.

Until now, the reactors used here were made in the form of a coaxial line or a wave guide. The conjugate reactance is then determined by the position of an inductive or capacitive discontinuity on the transmission line and by the more or less large value of this discontinuity. But high performance coaxial-line reactors can be made only up to 2 Gc and wave-guide reactors are of no interest to transistor devices.

On the other hand, for connection purposes, the lines habitually employed are equipped with intermediate coaxial plugs in order to link the reactor to the transistor which itself is equipped with coaxial plugs; this requires more and more connecting plugs. The

discontinuities introduced by the coaxial plugs and the lengthening of the distances between the transistor and the reactor create changes in the distribution of the stationary waves; these changes are also expressed by a drop in the precision in the evaluation of reactances.

SUMMARY OF THE INVENTION The device according to the invention makes it possible to avoid these inconveniences. In this device it is, in effect, possible to measure the exact impedance at the terminals of the transistors electrodes by limiting the intermediate connections to a minimum by using a reactor of a special type.

The invention concerns a reactor used in measuring the impedances of active circuits involving a microstrip transmission line, terminated by a first end capable of receiving energy from a signal generator and by a second end capable of transmitting this energy to said active circuits, and including further a variable reactance arranged on said microstrip capable of cancelling the reactance of the active circuits; said reactor is characterized by the fact that it includes a variable reactance which consists of a probe opposite said microstrip, both of which are contained in a box; this probe is associated with a screw that makes it possible to adjust its penetration with respect to said microstrip; this probe is equipped with two stops that rest on the bottom of said box and that exclude any ohmic contact with said microstrip; the penetration is then at a maximum and the assembly of probe and screw is in one piece with a trolley that can move along said microstrip.

According to another version of the invention, said variable reactance consists of two probes associated with two screws making it possible independently to adjust their penetration with respect to said microstrip; ohmic contact of the probe with the microstrip is excluded; each of the probe and screw assemblies constitutes one piece with two trolleys that can be moved independently along said microstrip.

Referring now to the attached figures, we will describe one example of implementing this invention; this example here is given purely by way of illustration and without any limitations. The same elements, shown on several figures, have been labeled with the same reference numbers on all figures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a perspective view of a reactor;

FIG. 2 shows a partial longitudinal cross section and a partial side view of the same reactor; and

FIG. 3 is a transverse cross section of the same reactor.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 we can see two micrometric screws land 2, arranged above a parallelepipedic box 3, revealing a longitudinal slot 4 on one upper face. Screws 1 and 2 are mounted on movable trolleys 5 and 6 which can slide along the longitudinal slot 4 independently of each other. A small scale 7, with graduations, is placed on one side of box 3 in order to make it possible to note the movements of the two slide contacts 5 and 6. Screws 8 and 9, which cannot be lost, make it possible to lock the slide contacts 5 and 6 at specific positions. Box 3 constitutes a wave guide which does not permit the transmission of TE and TM modes at the utilization frequencies of the reactor.

In FIGS. 2 and 3, we can see, inside box 3, a probe 10 whose penetration is controlled by screw 1. The screw penetrates into the interior of the box through the longitudinal slot.

A microstrip 11, consisting of a rigid conducting plate, is arranged at the bottom of the box 3. Microstrip 11 is supported on the end flanges l3 and 13 without touching the bottom of the box. The microstrip is electrically connected, at one if its ends, to the central core of a coaxial connector 12, provided for connections to a generator or a resistor load and, at-the other end, it is connected to a connector carried by flange 13, for the purpose of connection with a transistor. This connector includes a rod 14 which is split in two, suitable for receiving a flat electrode of a microwave transistor. Rod 14, connected to the microstrip 11, is arranged inside a circular conduit made in flange 13 which consists of aluminum or a similar substance. This flange, which is screwed on box 3, ensures electrical connection between the mass of the box and the transistor electrode which is connected to the mass.

The U-shaped probe 10 includes two stops l5 and 16. When the probe 10 is in the low position, these stops come to rest on the bottom of box 3, thus preventing the probe 10 from coming into contact with the upper face of microstrip 11. Probe 10 has such a configuration that we can avoid undesirable modes and resonances. In the high position, when screw 1 is unscrewed, a spring plate 17 prevents the screw and probe assembly from moving upward through slot 4. Two bars 20 and 21, arranged along the walls of box 3, ensure contact with probe 10 through springs 22 and 23. Because of this, electrical connection between the probe and the mass of the box opposite the microstrip is ensured by a short, indispensable, microwave path. Otherwise, the path between the probe and the box would be longer since it would pass through screw 1. Two other spring plates 18 and 19, arranged in the screw head and the screw support, make it possible to move screw 1 by switching. We thus can prevent excessive stresses which could exist in the low position, when the stops touch the bottom of the box. In the position, screw head 1 turns without advancing. In actual operation, we make the adjustments in order to obtain the optimum indications on the bolometer by beginning with the movement of one of the trolleys. We then adjust the height of screw 1. We then make the fine adjustment by moving the second trolley so that it will be placed half a wave length from the first trolley. We know in effect that, on a transmission line, identical conditions are reproduced at intervals equal to half a wave length.

We finish up by adjusting the screw of the second trolley. The assembly of the two trolleys thus permits rough adjustment followed by a particularly precise fine adjustment. Although the device just described seems most advantageous, it is to be understood that ble f rformi the e c ical unction.

'l e 'iactor iii volve d i n is ii i venti on can be used in all cases where we need to adapt the output and input impedances of a circuit presenting real (positive or negative) and imaginary terms. They can concern passive or active circuits requiring polarization by continuous currents superposed on a high-frequency.

Particularly interesting applications may involve the adaptation of the impedances of a transistor to microwaves.

What is claimed is:

l. A reactor for use in measuring impedances of active circuits comprising;

a. a microstrip transmission line;

b. first termination means coupled to said microstrip transmission line for receiving energy from a signal generator;

c. second termination means coupled to said microstrip transmission line for transmitting energy to active circuits;

d. a box enclosing said microstrip transmission line;

e. a variable reactance enclosed in said box and capable of cancelling the reactance of the active circuits, said reactor comprising;

i. a probe arranged in operable relationship with said microstrip transmission line;

ii. a screw means for adjusting the position of said probe relative to said microstrip;

iii. two stops for contacting said probe with the bottom of said box, said stops being such as to exclude any ohmic contact with said microstrip; and

iv. trolley means coupled to said probe and screw means to permit movement of said probe and screw means relative to said microstrip.

2. The reactor of claim 1 wherein said box has a rectangular cross-section at least partially open at one of its faces, said trolley being U-shaped overlapping said partly open face, said microstrip being situated within said box so that it does not rest on any of the sides of said box.

3. The reactor according to claim 1, wherein said screw means includes a friction head for moving said screw means.

4. The reactor according to claim 1, further including a second variable including a second probe and screw means, said first and second screw means permitting independent adjustment of said first and second probes and second trolley means for moving said second probe and screw means, movement of said first and second trolleys being independent of each other.

5. The reactor according to claim 1, wherein said first termination means includes a coaxial connector and wherein said second termination means includes a central conductor for receiving a flat electrode of a transistor, said conductor being conducted to said microstrip. 

1. A reactor for use in measuring impedances of active circuits comprising; a. a microstrip transmission line; b. first termination means coupled to said microstrip transmission line for receiving energy from a signal generator; c. second termination means coupled to said microstrip transmission line for transmitting energy to aCtive circuits; d. a box enclosing said microstrip transmission line; e. a variable reactance enclosed in said box and capable of cancelling the reactance of the active circuits, said reactor comprising; i. a probe arranged in operable relationship with said microstrip transmission line; ii. a screw means for adjusting the position of said probe relative to said microstrip; iii. two stops for contacting said probe with the bottom of said box, said stops being such as to exclude any ohmic contact with said microstrip; and iv. trolley means coupled to said probe and screw means to permit movement of said probe and screw means relative to said microstrip.
 2. The reactor of claim 1 wherein said box has a rectangular cross-section at least partially open at one of its faces, said trolley being U-shaped overlapping said partly open face, said microstrip being situated within said box so that it does not rest on any of the sides of said box.
 3. The reactor according to claim 1, wherein said screw means includes a friction head for moving said screw means.
 4. The reactor according to claim 1, further including a second variable including a second probe and screw means, said first and second screw means permitting independent adjustment of said first and second probes and second trolley means for moving said second probe and screw means, movement of said first and second trolleys being independent of each other.
 5. The reactor according to claim 1, wherein said first termination means includes a coaxial connector and wherein said second termination means includes a central conductor for receiving a flat electrode of a transistor, said conductor being conducted to said microstrip. 